Mac Réamoinn entered the Irish diplomatic service in 1944. He transferred to Radio Éireann, then a part of the civil service, when the station was expanded in 1947. For several years he was part of the outside broadcast unit along with Seamus Ennis and travelled the country recording and collecting folklore. He helped the revival of Irish traditional music through introducing regional styles to a national audience and providing a platform for young musicians.[1]

He became a member of the station's governing body, the RTÉ Authority. From 1962 to 1965, he reported on the Second Vatican Council.[1]

Mac Réamoinn regularly wrote for newspapers and magazines in both Irish and English. He was a member of the editorial board of Scripture in Church since its beginnings, in the Spring of 1971.